Lightweight (only 3.5 pounds) and bendable, the “arm” attaches to the user’s back hip, resembling a camera rig—or something out of Aliens. The current mock-up can support weapons up to 27 pounds, as well as a 20-pound defensive shield.

“We started out with just trying to think of a way to help improve the lethality for the dismounted soldier,” ARL engineer Dan Baechle said in a statement. “Generally that means stabilizing the weapon or giving the soldier a more powerful weapon.”

Researchers opted for the former.

Their “third arm” was put to the test last summer, when a six-soldier team—dotted with electromyography sensors to measure muscle activity—fired weapons with and without the apparatus.

Soldiers can attach the apparatus to a shield for added stability and balance (via Joe Lacdan/U.S. Army)

“We found that it reduced the fatigue and reduced the muscle activation for some soldiers,” Baechle said.

A larger trial with up to 15 volunteers is scheduled for this spring.

The data is easily verified: Simply hold a weight in an outstretched hand, and after a few moments your arm will start shaking. Now imagine you’re trying to aim and fire a deadly weapon with that wobbly arm.

Additional adjustments aim to make the device more comfortable, further reduce fatigue, and boost a shooter’s accuracy. Engineers also hope to reduce some of the recoil force of firing a weapon.

“You have a lighter-weight weapon but potentially a higher caliber weapon which normally would increase the recoil on your shoulder,” Baechle explained.

“Could you use Third Arm and some clever materials on the arm to redirect the recoil back toward the body and thus allow the soldier to wield a higher-energy weapon without necessarily burdening the soldier more?”